Crosslinkable composition comprising aminoepoxy resin-IV

ABSTRACT

A self-crosslinkable resin and a composition of matter comprising same are provided, which resin comprises certain diene functional blocked dieneophile functional aminopoxy resin, which resin is self-crosslinkable at elevated cure temperature. The diene functional blocked dieneophile functional aminoepoxy resin comprises the reaction product of diepoxide with amine functional diene chain extending reactant, amine functional blocked dieneophile chain extending reactant, optionally, monofunctional end-capping reactant such as mono-secondary amine functional diene and mono-secondary amine functional blocked dieneophile, and modifying agent comprising hydroxy functional secondary amine. Compositions comprising the aforesaid self-crosslinkable resin may further comprise crosslinking agent reactive with hydroxy functionality of the resin. The crosslinkable composition of matter is useful in coatings and other applications, especially solvent-based primer coating compositions and cathodic electrocoating compositions.

TECHNICAL FIELD

The invention relates to a novel self-crosslinking resin and to acomposition of matter comprising same. Specifically, certain dienefunctional blocked dieneophile functional aminoepoxy resin isself-crosslinking at elevated cure temperatures. According to certainpreferred embodiments, this invention relates to use of such resincomposition to form corrosion protective coatings. This inventionespecially relates to one-component solvent based primer coatingcomposition comprising such resin and to aqueous coating compositionadapted for use in cathodic electrodeposition processes.

RELATED APPLICATIONS

This application is related to applications Ser. Nos. 565,798, now U.S.Pat. No. 4,559,393, 566,063, now U.S. Pat. No. 4,565,852 and 566,068filed Dec. 27, 1983, now U.S. Pat. No. 4,582,880. In addition, thefollowing commonly assigned applications each relate todiene/dieneophile chemistry in compositions suitable for thermosettingcoatings and the like: Ser. Nos. 455,678, now U.S. Pat. No. 4,514,548and 455,718 filed Jan. 1, 1983, now U.S. Pat. No. 4,514,549, Ser. Nos.456,067, now U.S. Pat. No. 4,515,926 and 456,068 filed Jan. 6, 1983, nowU.S. Pat. No. 4,513,125, and Ser. No. 458,119 filed Jan. 14, 1983, nowU.S. Pat. No. 4,508,879.

BACKGROUND ART

Coating compositions are known which are suitable for application to asubstrate, for example, by spraying, dipping electrodeposition or thelike, which coating compositions are then cured by baking the coatedsubstrate at an elevated temperature. Typically, such coatingcompositions comprise resinous materials or blends of resinousmaterials, in some cases together with suitable crosslinking agentreactive with such resinous materials at elevated temperature.

In regard to electrodeposition of coatings, the process is welldescribed in the art. Typically, an aqueous bath containing the coatingcomposition is placed in contact with an electrically conductive anodeand an electrically conductive cathode, and upon the passage of electriccurrent (normally direct current) between the anode and the cathode, anadherent film of the coating composition is deposited. Depending uponthe nature of the coating composition, the coating may be deposited atthe anode or at the cathode. The voltage applied may vary from as lowas, for example, one volt to as high as, for example, 500 volts orhigher. Typically, however, the voltage used ranges from about 50 toabout 400 volts.

A wide variety of electrodepositable resins are known to the skilled ofthe art. For example, a number of water-soluble, water-dispersible, orwater-emulsifiable poly-carboxylic acid resins can be electro-deposited.Some of these resins include, for example, reaction products or adductsof a drying oil or semi-drying oil fatty acid ester with a di-carboxylicacid or anhydride; interpolymers of a hydroxyalkyl ester of anunsaturated carboxylic acid, unsaturated carboxylic acid, and at leastone other ethylenically unsaturated monomer; alkyd-amine vehicles, thatis vehicles containing an alkyd resin and an amine-aldehyde resin; andmixed esters of resinous polyols. In U.S. Pat. No. 3,991,028 to Irwin etal, electrodepositable compositions are disclosed which comprise awater-dispersion of a hydrolyzed polyepoxide in combination with aninter-polymer of a hydroxyalkyl ester, an unsaturated acid and at leastone other monomer, and an amine-aldehyde resin. The use of a hydrolyzedpolyepoxide is said to provide improved properties and to avoidagglomeration of the coating composition. In U.S. Pat. No. 4,026,855 toParekh et al, a coating composition is disclosed to be adaptable for usein electrodeposition or as a water-based coating for applicatin by sprayor dip coating methods. The composition comprises an aqueous dispersionof (A) an ungelled modified crosslinking agent comprising certainaminoplast crosslinking agent modified by reaction with a non-resinouscompound containing an hydroxyl-group bearing carboxylic acid, and (B) awater-dispersible non-gelled polymeric material carrying a cationiccharge and containing at least one class of reactive groups selectedfrom carboxyl groups, alcoholic hydroxy groups and amide groups and alsocontaining amino groups, and (C) an acid solubilizer. In U.S. Pat. No.4,033,917 to Sekmakas et al, certain copolymers of polyethylenicallyunsaturated epoxy-amine adducts are disclosed and also stable aqueousdispersions containing same and also the electrodeposition of suchaqueous dispersions at the cathode of a unidirectional electricalsystem. Specifically, amine functional polymers dispersible in waterwith the aid of a solublizing acid are said to be provided bycopolymerizing (A) certain ethylenically unsaturated hydroxy functionalamine adduct free of epoxy groups; and (B) copolymerizablemonoethylenically unsaturated monomers, a portion of which isamine-functional. The copolymer is said to be stably dispersible inwater at certain pH and to be electrodepositable at the cathode,optionally together with an aminoplast curing agent to provide coatingswhich can be cured, ususally by exposure to elevated temperature. U.S.Pat. No. 3,471,388 to Koral is directed to a cathodic electro-coatingcomposition which incorporates an aminoplast crosslinker (e.g.,butylated melamine) with an aminated polymer containing hydroxy groups.Numerous suitable hydroxy-containing aminated polymers are suggestedwhich have capability to crosslink with an aminoplast crosslinkingagent. One such suggested polymer is the reaction product of apolyfunctional amine with a polyfunctional epoxy compound. Thepolyhydroxy polymers are said to be disperable in water upon addition ofsuitable acid such as acetic acid.

Additional teaching directed to coating compositions suitable for use inelectrocoating processes is provide in U.S. Pat. No. 4,159,233 to Tingeet al; U.S. Pat. No. 4,057,523 to Blank; U.S. Pat. No. 4,182,831 toHicks; U.S. Pat. No. 4,192,932 to Dickie, which patent is assigned tothe assignee of the present application; U.S. Pat. No. 4,192,929 toBloomfield, which patent is assigned to the assignee of the presentapplication; U.S. Pat. No. 4,202,746 to Lee et al; and U.S. Pat. No.4,072,536 to Otsuki et al.

It is a general objective of the present invention to provide acomposition of matter adaptable for use in coating compositions,including compositions adapted for use in solvent-based sprayablecoating compositions, compositions adapted for use in electro-depositioncoating compositions, and compositions adapted for use in themanufacture of adhesives, molding compounds and textile treating resinsand the like. Additional objects and aspects of the present inventionwill be apparent from the following description thereof.

DISCLOSURE OF THE INVENTION

The present invention provides a self-crosslinking resin, specifically,a substantially gelfree diene functional blocked dieneophile functionalaminoepoxy resin, preferably of number average molecular weight (Mn)about 1000-9000. Such aminoepoxy resin is the reaction product ofsuitable diepoxide reactant with reactants comprising (i) aminefunctional diene chain extending reactant, (ii) amine functional blockeddieneophile chain extending reactant, (iii) optionally, end-cappingreactant, and (iv) hydroxy functional secondary amine modifying agent.Preferably, the aminoepoxy resin of the invention is prepared by firstreacting an excess of diepoxide reactant with the aforesaid chainextending reactants and, optionally, end-capping reactants, and bysubsequently reacting the resulting epoxy functional intermediateproduct with the aforesaid modifying agent, preferably secondaryalkanolamine, in approximately 1:1 ratio of epoxy functionality to aminefunctionality.

Specifically, the chain extending reactants comprise (i) aminefunctional diene, particularly di-secondary amine functional bis-dieneor, more preferably, mono-primary amine functional diene, for examplefurfuryl amine, or a mixture thereof, and (ii) amine functional blockeddieneophile, particularly di-secondary amine functional bis-blockeddieneophile or, more preferably, mono-primary amine functional blockeddieneophile, for example amino maleamic acid, or a mixture thereof.Suitable end-capping reactants include monofunctional reactants, thatis, reactants bearing a single functionality substantially reactive withepoxy functionality of the chain extended resin. The term"monofunctional" in this usage, however, is not intended to be exclusiveof diene functionality or dieneophile functionality. Thus, suitableend-capping reactants include monofunctional diene reactants, forexample mono-secondary amine functional diene reactants and monohydroxyfunctional diene reactants, and mono-functional blocked dieneophilereactants, for example mono-secondary amine functional blockeddieneophile reactants and monohydroxy functional blocked dieneophilereactants, and any mixture thereof. Suitable hydroxy functionalsecondary amine modifying agents for reaction with the aforesaid epoxyfunctional intermediate reaction product are further discussed below.

The self-crosslinkable resin of the invention is particularly useful incoating compositions and according to preferred embodiments furtherdiscussed below is readily adaptable for use in solvent-based coatingcompositions and in aqueous-based electrodeposition coatingcompositions. Coatings provided by the present invention are found to behighly resistant to solvents and humidity and to provide exceptionalcorrosion protection for the underlying substrate. The invention isparticularly advantageous in that it provides coatings which cure atrelatively low temperature. The self-crosslinkable resin of theinvention also may be used in the manufacture of low pressure laminates,adhesives, molding compounds, textile treating resins and the like.

According to a significantly advantageous aspect of the invention, themolecular weight of the self-crosslinkable aminoepoxy resin is readilycontrollable to suit an intended application. Thus, for use in acathodic electrocoating composition, for example, the aminoepoxy resinis readily provided having preferred number average molecular weight(Mn) of about 1000-9000; for use in solvent-based sprayable coatingcompositions, such resin is readily provided having preferred numberaverage molecular weight (Mn) of about 1000-4000. Such molecular weightcontrol is achieved by selection of diepoxide reactant havingappropriate epoxide equivalent weight and/or by adjusting the molarratio of diepoxide to chain extension reactants to end-cappingreactants. Lower molecular weight resin is provided as such ratioapproaches 2:1:1, respectively; higher molecular weight resin isprovided as it approaches 1:1:0. Of course, as noted above, astoichiometric excess of diepoxide reactant is used to provide epoxyfunctionality for reaction with the hydroxy functional secondary aminemodifying agent.

The self-crosslinkable composition of the present invention isparticularly suitable for use in solvent-based sprayable primer coatingcompositions. Such primer compositions can be used, for example, to formheat curable, highly alkali resistant primer coatings on automotivevehicle body panels. For such use the aminoepoxy resin is preferably ofnumber average molecular weight about 1000-3000. The composition can bethinned to desired viscosity with suitable solvent such as, for example,methyl amyl ketone.

The self-crosslinkable composition of the present invention also can beadapted for use in cathodic electrodeposition. For such use, theaminoepoxy resin is preferably of number average molecular weight (Mn)above about 1000, more preferably about 1000-9000, and is at leastpartially neutralized with a solubilizing acid, typically an organicacid such as, for example, acetic acid or the like. The at leastpartially neutralized resin is then dispersed in aqueous solvent. Suchcoating composition will deposit a heat curable coating at the cathodein an electrodeposition coating process according to techniques wellknown to the skilled in the art.

Other features and advantages of the present invention will become moreapparent from the following detailed description including the preferredembodiments and best mode of the invention.

DETAILED DESCRIPTION OF THE INVENTION Diepoxide Reactant

Suitable diepoxide reactants include any of a wide variety of diepoxideknown to the skilled of the art, for example aliphatic and aromaticdiepoxide resins. The diepoxide reactant preferably has epoxideequivalent weight of about 150-2000. In general, the epoxide equivalentweight is selected to suite the intended use of the final composition.Thus, for sprayable solvent-based coating compositions a lowercomposition viscosity is desirable. For such use it is generallypreferable to employ diepoxide having epoxide equivalent weight of about150-1000. In comparison, for example, cathodic electrodepositioncompositions of the invention preferably have higher viscosity and forsuch use diepoxides having epoxide equivalent weight of about 150-2000are generally preferred.

The diepoxide is preferably free of carboxy ester moieties linking theepoxide groups, since such carboxy ester-free diepoxides have been foundto provide cured coatings according to the invention which aresignificantly more alkali resistant and provide significantly enhancedcorrosion protection to the underlying substrate.

One class of suitable diepoxides includes the BisphenolA-epichlorohydrin resins. These are commercially available as, forexample, Epon 828, 1001 or 1004 (trademarks) marketed by Shell ChemicalCompany, Houston, Tex., U.S.A. Suitable diepoxides may contain aromaticgroups, such as benzene nuclei, at a preferred average of at least aboutone, more preferably at least about two, for each terminal epoxy group.Especially suitable are Bisphenol A-epichlorohydrin resins comprising upto 10 or more bis-phenol moieties within the epichlorohydrin reactionproduct backbone, for example those of number average molecular weightup to about 8000, preferably 300-4000.

Aliphatic diepoxides, particularly lower molecular weight aliphaticdiepoxides, including cycloaliphatic diepoxides are used preferably inconjunction with aromatic diepoxides to modify coating properties.Certain lower molecular weight aliphatic diepoxides used alone mayproduce coatings which are relatively more humidity sensitive. Suitablealiphatic diepoxides include, for example, the reaction product ofepihalohydrin with aliphatic diols such as glycol, epoxidizedpolybutadienes, vinylcyclohexenedioxide and dipentene dioxide. Stillfurther, hydrogenated Bisphenol A-epichlorohydrin products may also beemployed.

Numerous additional suitable diepoxides are commercially available orreadily prepared using well known techniques and commercially availablestarting materials, and these will be apparent to the skilled of the artin view of the present disclosure. Compatible mixtures of any of thesecompound also are suitable.

AMINE FUNCTIONAL DIENE CHAIN EXTENDING REACTANT

Amine functional dienes suitable for use in preparing the resin of thepresent invention are those comprising conjugated double bonds,particularly, those suitable for Diels Alder cycloaddition reaction atelevated temperature with ene-functionality or with other dieneophilefunctionality. Suitable amine functional dienes include many well knownto the skilled of the art. Preferred are monoprimary amine functionaldienes, preferably of molecular weight about 70-300 and preferablycomprising no functionality substantially reactive with the diepoxide,other than the N-hydrogens. Exemplary monoprimary amine functionaldienes include furfuryl amine, 2-aminomethyl-1,3-butadiene, and the likeand a mixture thereof. Suitable di-secondary amine functional bis-dieneswill be apparent to the skilled of the art in view of the presentdisclosure and can be prepared readily using well known techniques andcommercially available reactants.

The amine functional diene preferably is monoprimary amine functionaldiene according to formula I: ##STR1## wherein:

R is a monoprimary amine functional hydrocarbon moiety, which preferablycomprises no functionality substantially reactive with the diepoxidereactant other than the amine functionality; and ##STR2## or the like,wherein R¹ is hydrogen, straight, branched or cyclo alkyl, aryl,arylalkyl or the like, and each R² is the same or different and isselected from hydrogen, hydroxy, carboxy, straight, branched orcycloalkyl, aryl, arylalkyl, and the like, each alkyl, aryl or arylalkylmoiety of R¹ and R² being unsubstituted or mono or poly-hydroxysubstituted or mono or poly-amino substituted; and

X¹, X², X³, X⁴ and X⁵ are the same or different and each is hydrogen,hydroxy, carboxy, amino, straight, branched or cyclo alkyl, aryl,arylakyl, cyano, nitro, or the like, or X¹ and X⁵ together are alkylene,--O--, --NR¹ -- wherein R¹ is as defined above, or like divalent group(resulting in a cyclic diene moiety), each alkyl, aryl, arylalkyl andalkylene moiety of X¹, X², X³, X⁴ and X⁵ being unsubstituted or mono- orpoly-hydroxy substituted or mono- or polycarboxy substituted or mono- orpoly-amino substituted.

According to one most preferred embodiment, the monoprimary aminefunctional diene reactant is of the general formula: ##STR3## wherein R³is a divalent organic linking moiety containing no ester groups and nofunctionality substantially reactive (under reaction conditionsexperienced by the amine functional diene reactant in the preparation ofthe aminoepoxy resin) with the other reactants.

The reaction product, that is, the aminoepoxy resin, comprises, onaverage, at least one diene moiety per molecule. Each diene moiety willbe available for reaction with a dieneophile moiety of the resin duringheat curing of a composition according to the inventon. More preferably,the aminoepoxy resin provides, on average about two or more, such asabout 2-10 diene moieties per molecule.

Amine Functional Blocked Dieneophile Chain Extending Reactant

The aminoepoxy resin of the invention preferably comprises, on average,at least about 1, preferably about 2-10, blocked dieneophile groups permolecule. The blocked dieneophile groups are capable of reacting withthe diene moieties of the aminoepoxy resin upon curing the compositionat elevated temperature, typically about 100° C.-200° C. Preferably thedieneophile moiety is an ene moiety although other suitable dieneophilemoieties will be apparent to the skilled of the art in view of thepresent disclosure.

According to a preferred embodiment of the invention, the aminefunctional blocked dieneophile reactant comprises mono-primary aminefunctional blocked dieneophile reactant. The mono-primary aminefunctional blocked dieneophile reactant is preferably the reactionproduct of maleic anhydride, unsaturated lactone, or a compatiblemixture thereof with a suitably reactive diene, and a suitably reactivediamine. The diene reactant acts as a reversible blocking agent for thedieneophile functionality and such reaction can be carried out prior to,during or after the reaction with the diamine. The diene reactantpreferably has a boiling point at or below the cure temperature of thecoating composition such that it will be driven from the coatingcomposition during cure thereof, and not compete with the dienefunctionality of the aminoepoxy resin for reaction with the dieneophilefunctionality. To maximize yield of mono-primary amine functionalblocked dieneophile, it is preferred to add the anhydride or lactonereactant slowly to an excess of diamine reactant.

According to one prefered embodiment, the monoprimary amine functionalblocked dieneophile reactant comprises amino maleamic acid,specifically, the reaction product of suitable diamine with3,6-endoxo-1,2,3,6tetrahydrophthalic anhydride. The named anhydride iscommercially available, for example from Aldrich Chemical Co.,Milwaukee, Wis., U.S.A. and also can be prepared as the reaction productof furan with maleic anhydride.

More generally, suitable amine functional blocked dieneophile reactantcomprises the reaction product of (i) suitable diamine, and (ii)suitable conjugated diene reversible blocking agent, with (iii) enereactant selected from the group consisting of maleic anhydride,suitable unsaturated lactones or the like or any compatible mixturethereof, wherein the lactone preferably is selected from those of thegeneral formula: ##STR4## wherein each R' is selected independently fromH, C₁ -C₅ alkyl, C₁ -C₅ hydroxy alkyl and the like, and y is preferablyabout 1-4. Numerous suitable diamines are commercially available andwill be apparent to the skilled of the art in view of the presentdisclosure. Suitable diamines include those of the general formula H₂N--R⁵ --NH₂ wherein R⁵ is any divalent organic linking moiety of atleast two carbons, preferably 2-15 carbons, which is substantiallyunreactive (under conditions experienced by the amine functional blockeddieneophile reactant in the preparation of the aminoepoxy resin) withthe other reactants. Included are branched, straight and cyclicaliphatic diamines, aromatic diamines and arylaliphatic diamines.Exemplary diamines include isophorone diamine which is preferred in viewof the difference in reactivity of the two amine groups resulting inhigher yield of the desired product, 1,4-butanediamine,1,5-pentanediamine, 1,6-hexanediamine, and a compatible mixture of anyof them. Other preferred diamines include those of molecular weightabout 80-300 which comprise no substantially reactive functionalityother than amine. Exemplary such diamines include 1,2-ethylenediamine,1,3-propanediamine, the isomers of toluene diamine and the like and acompatible mixture of any of them.

Suitable conjugated diene blocking agents include numerous commerciallyavailable dienes readily apparent to the skilled of the art in view ofthe present disclosure. Included are any sufficiently reactiveconjugated aliphatic, cyclic aliphatic, and heterocyclic dienes whichwill liberate or de-block from the dieneophile moiety at the curetemperature of the coating composition. The diene blocking agent shouldbe substantially unreactive with the other reactants except for thedieneophile functionality of the ene reactant. Exemplary conjugateddiene blocking agents include furan which is preferred since itde-blocks at approximately 120° C., conjugated cycloalkadiene such as1,3-cyclopentadiene and 1,3-cyclohexadiene, conjugated alkadienepreferably of about 4-10 carbons, for example, 1,3-butadiene,2-methyl-1,3-butadiene, and the like and a compatible mixture of any ofthem. The reactions described above for preparation of the aminefunctional blocked dieneophile crosslinking agent can be conductedaccording to methods well known to the skilled of the art. It should benoted that where symmetrical diamine is employed, such as1,6-hexanediamine, rather than diamine wherein one amino group issubstantially more reactive than the other, such as isophorone diamine,there can be a portion of the diamine reactant in which both aminegroups remain unreacted due to reaction of both amine groups of anotherportion of the diamine reactant. To prevent subsequent unwanted aminereactions and gelling, substantially all unreacted diamine should beremoved from the reaction product. Removal of diamine can be done bymethods known to the skilled of the art, for example by thorough rinsingof the reaction product with dimethoxy ethane or other suitable solvent.

END-CAPPING REACTANT

The aminoepoxy resin of the invention preferably is end-capped byreaction with suitable monofunctional reactant. Preferred aremonofunctional diene reactants and monofunctional blocked dieneophilereactants, of molecular weight about 70-300, included among which aremany well known to the skilled of the art. Exemplary such end-cappingreactants include mono-secondary amine functional diene, monohydroxyfunctional diene, monosecondary amine functional blocked dieneophile,monohydroxy functional blocked dieneophile, and any mixture thereof. Asnoted above, the term monofunctional in this usage is intended to mean asingle functionality substantially reactive with epoxy functionality andis not exclusive of diene or dieneophile functionality. Especially wherethe aminoepoxy resin is already both diene and blocked dieneophilefunctional, the monosecondary amine functional end-capping reactantsgenerally are preferred over mono-hydroxy functional reactants in viewof the milder reaction conditions required for amine-epoxy reaction.Preferably no more than about 10-20% of the total epoxide functionalityis reacted with end-capping reactant. As noted above, however, the molarratio of reactants can be varied to provide aminoepoxy resin of desiredmolecular weight. The chain extended diepoxide reactant is reacted withthe end-capping agent, if any, according to methods well known to theskilled in the art. Accordingly, for example, the chain extendeddiepoxide is mixed with the end-capping agent and the mixture is heatedto reaction temperature, typcially above 60°-80° C., until substantiallyall epoxide functionality has reacted.

Suitable monofunctional diene end-capping agents include those offormula I: ##STR5## wherein:

R is a monohydroxy functional hydrocarbon moiety or a mono-secondaryamine functional hydrocarbon moiety, respectively, which comprises nofunctionality substantially reactive with the chain extended diepoxidereactant other than the hydroxy or secondary amine functionality; and##STR6## or the like, wherein R¹ is hydrogen, straight, branched orcycloalkyl, aryl, arylalkyl or the like, and each R² is the same ordifferent and is selected from hydrogen, straight, branched or cyclo-alkyl, aryl, arylalkyl, and the like; and

X¹, X₂, X³, X⁴ and X⁵ are the same or different and each is hydrogen,straight, branched or cyclo alkyl, aryl, arylakyl, or the like, or X¹and X⁵ together are alkylene, --O--, --NR¹ -- wherein R¹ is as definedabove, or like divalent group (resulting in a cyclic diene moiety).Exemplary monohydroxy dienes include furfuryl alcohol and2-hydroxymethyl-1,3-butadiene and the like and any compatible mixturethereof.

Preferred monofunctional blocked dieneophile end-capping reactantsinclude the reaction product of a suitable diene blocking agent, asdescribed above, such as furan, cyclopentadiene, and the like, withmonohydroxy functional or mono-secondary amine functional dieneophilesuch as, for example, hydroxypropyl methacrylate, methylol maleimide orthe like or a compatible mixture thereof. Again, since suchmonofunctional end-capping reactant provides only end-capping and notchain-extending reaction with the diepoxide, self-crosslinkingaminoepoxy resin of lower molecular weight can be provided according tothis embodiment. Such lower molecular weight resin is particularlyadvantageous for use in sprayable solvent-based coating compositions.

The amine functional blocked dieneophile and the amine functional dienereactants can be reacted simultaneously with the diepoxide, butpreferably are reacted sequentially. If reacted simultaneously, it willbe within the skill of the art to select suitable molar ratios, in viewof the relative reactivity of the reactants, to achieve the desireddegree of diene and blocked dieneophile functionality in the productamino-epoxy resin. It is generally preferred to react sequentially,since this is found to provide a resin product of narrower molecularweight range. It is generally preferred that the diene functionality andthe blocked-dieneophile functionality of the self-crosslinkingaminoepoxy resin of the invention be present in a ratio of approximately1:2 to 2:1, respectively, and most preferably such ratio is about 1:1.The end-capping reactant(s) can be employed either simultaneously withor, more preferably, subsequently to the chain-extension reactants. Ifreacted simultaneously, it will be within the skill of the art to selectsuitable reactant ratios, in view of their relative reactivities, toproduce an aminoepoxy resin product having the desired number averagemolecular weight and having the desired degree of functionality.

Modifying Agent

As noted above, according to one characterizing aspect of this inventionthe diepoxide reactant is employed in stoichiometric excess relative tothe amine functional diene reactant, amine functional blockeddieneophile reactant and, if any, the end capping reactant. The excessepoxy functionality is available for reaction with a modifying agent.According to this aspect of the invention, the diepoxide is reactedpreferably in an amount sufficient to provide about 10%-20% excess freeepoxy equivalent for each equivalent, in total, of amine functionaldiene, amine functional blocked dieneophile and end-capping agent (ifany). The excess epoxy functionality is reacted with the modifyingagent.

The modifying agent comprises hydroxy functional secondary amine havinga total of up to about 20 carbons per amino nitrogen More preferably, atleast about 75 mole percent of the modifying agent comprises at leastone and preferably two primary hydroxyl groups, each hydroxyl group on acarbon atom being at least one carbon removed from any amino nitrogen.Preferred secondary amine reactants include, for example,alkylalkanolamine, dialkanolamine, N-alkanolaniline and the like and acompatible mixture of any of them, wherein each alkyl moiety and eachalkanol moiety has from one to about ten carbons, more preferably one toabout six carbons. Most preferred are the C₁ -C₅ dialkanolamines,especially diethanolamine, in view of their ready commercialavailability, low cost, and ease of reaction with the preferredpolyepoxides. While not wishing to be bound by theory, it is presentlyunderstood that each hydroxy group contributed by the modifying agent tothe resin product is available for polar-polar interaction with aqueoussolvent, thereby enhancing the dispersibility of the resin in theaqueous solvent and rendering the aqueous dispersion more stable. It isbelieved to be consistent with such explanation that dialkanolaminebearing two primary hydroxy groups is found to provide exceptionallygood results

A preferred class of hydroxy functional secondary amine modifying agentsincludes those of general formula: ##STR7## wherein each R" is selectedindependently from straight or branched chain monovalent aliphaticmoieties of up to about 10 carbons each, at least one and preferablyboth R" being substituted by hydroxy on a primary carbon atom that isnot adjacent to any amino nitrogen. R" also can form with the nitrogenpart of a heterocyclic ring compound, such as a six member ring. Morepreferably, both R" are independently alkanol of up to 7 carbons each,even more desirably up to 4 carbons each.

The chain extended diepoxide and the hydroxy functional secondary aminemodifying agent are reacted under conditions that allow opening of theepoxy ring by amino nitrogen to provide a gel-free reaction product.Suitable reaction conditions and techniques are well known to theskilled of the art and will be apparent from the present disclosure.Thus, for example, the reaction medium preferably comprises non-aqueousmedium that may be of diverse but preferably polar character and servesto maintain contact of reactants, control reaction speed, maintaindesirable viscosity and to perform other functions well known in theart. Thus, suitable solvents and diluents for the reaction mediuminclude aromatic and aliphatic hydrocarbons, halides, ethers, ketonessuch a methylamyl ketone, n-amyl ether, xylene, oxygenated solvents suchas cellosolves, for example, butyl Cellosolve acetate, hexyl Cellosolveacetate, and the like including mixtures of these. Elevated reactiontempertures may be employed to faciliate reaction between the epoxyfunctional resin and the modifying agent, but the reactants preferablyare used in stoichiometric amounts (i.e., the resin and modifying agentare reacted in substantially 1:1 epoxy to amine equivalent ratio) andthe reaction conditions are chosen such that there is only one reactionbetween the intermediate reaction product and the modifying agent,specifically, that between the N-hydrogen of the modifying agent and anepoxide ring of the resin. It is preferred that sufficient secondaryamine reactant be used to react substantially all epoxy functionality ofthe resin. More specifically, for example, about 0.9-1.0 amineequivalent of the modifying agent is reacted with about 1 to 1:1equivalent epoxy functionality. More specifically, the reaction productshould contain less than about 20% of the original unreacted epoxygroups, more desirably about 10%-20%

Crosslinking Agent

Although the resin of the invention is self-crosslinking, additionalcrosslinking agent may be employed. The diene functional blockeddieneophile functional aminoepoxy resin provides free hydroxy groups asa result of the amine/epoxy reactions. In addition, the hydroxyfunctional secondary amine modifying agent contributes hydroxyfunctionality. Therefore, according to one embodiment of the inventionthe crosslinkable composition further comprises suitable crosslinkingagent reactive with such hydroxy groups. Numerous such crosslinkingagents are well known to the skilled of the art and include, forexample, any of a variety of aminoplast crosslinking agents, forexample, partially alkylated melamines (melamines formaldehyde resinsmodified by alcohols), for example, partially methylated melamines andbutylated melamines, polyalkyl ethers of the polymethylol melamines, forexample, hexamethoxy methylmelamine; urea formaldehyde condensatemodified by alcohol, for example, paraformaldehyde and trioxane;polymethylol compounds of hexamethylene diurea; polycarboxylic acid suchas adipic acid and the dimethylol amide and methylol ether thereof;tetramethylolhydrazodicarbonamide; polymethylol compounds ofpolycaprolactam and methylol ethers thereof; and the like and acompatible mixture of any of them. Butylated melamines are preferredsince they are readily commercially available and provide suitablecrosslinking reactivity with the aminoepoxy resin of the invention.

Also suitable are blocked polyisocyanate crosslinking agents. As usedherein "blocked polyisocyanate" means an isocyanate compound containingtwo or more isocyanato groups, each of which has been reacted with ablocking agent which will prevent reaction of the isocyanate group atroom temperature with compounds that conventionally react with suchgroups, and at least some of which will permit that reaction to occur athigher (cure) temperatures. In general, the blocked polyisocyanate maybe prepared by reacting a sufficient quantity of an active hydrogencontaining blocking agent with the polyisocyanate to insure thatsubstantially no free isocyanato groups are present.

The proper proportion of blocked polyisocyanate crosslinking agent toaminoepoxy resin will depend, in part, upon the degree of hydroxyfunctionality of such resin, the properties desired in the coating to beproduced and, in part, upon the desired cure response of the coatingcomposition (which will depend, in turn, upon the baking schedule to beused in curing the coating composition) and, in part, upon the desiredstorage stability of the composition, that is, upon the desired shelflife. Accordingly, the amounts of such crosslinker that can be usedvaries considerably. However, it will be within the skill of the art inview of the present disclosure to provide blocked polyisocyanatecrosslinking agent in suitable amounts Blocked polyisocyanates ofnumerous types may be employed in the compositions of the invention.Particularly suitable blocked polyisocyanates, which will be discussedfurther hereinafter, include blocked polymethylene polyphenolisocyanates, isocyanurate ring containing blocked polyisocyanates andcertain oligoester modified blocked polyisocyanates.

In the preparation of the blocked polyisocyanate crosslinking agent, anysuitable organic polyisocyanate may be used. Representative examplesinclude the aliphatic compounds such as trimethylene, tetramethylene,pentamethylene, hexamethylene, 1,2-propylene, 1,2-butylene,2,3-butylene, 1,3-butylene, ethylidene and butylidene diisocyanates; thecycloalkylene compounds such as 1,3-cyclopentane, 1,4-cyclohexane, and1,2-cyclohexane diisocyanates; the aromatic compounds such asm-phenylene, p-phenylene, 4,4'-diphenyl, 1,5-naphthalene, and1,4-naphthalene diisocyanates, the aliphatic-aromatic compounds such as4,4'-diphenylene methane, 2,4- or 2,6-tolylene, or mixtures thereof,4,4'-toluidine, and 1,4-xylylene diisocyanates; substituted aromaticcompounds such as dianisidine diisocyanate, 4,4'-diphenyletherdiisocyanate and chlorodiphenylene diisocyanate; the triisocyanates suchas triphenyl methane-4,4'4"-triisocyanate, 1,3,5-triisocyanate benzeneand 2,4,6-triisocyanate toluene; the tetraisocyanates such as4,4'-diphenyl-dimethyl methane-2,2',5,5'tetraisocyanate; and thepolymerized polyisocyanates such as tolylene diisocyanate dimers andtrimers, and the like.

In addition, the organic polyisocyanate may be a prepolymer derived froma polyol including polyether polyol or polyester polyol, includingpolyethers which are reacted with excess polyisocyanates to formisocyanate-terminated prepolymers. The polyols may be simple polyolssuch as glycols, e.g., ethylene glycol and propylene glycol, as well asother polyols such as glycerol; tri-methylolpropane, pentaerythritol,and the like, as well as mono-ethers such as diethylene glycol,tripropylene glycol and the like and polyethers, i.e., alkylene oxidecondensates of the above. Among the alkylene oxides that may becondensed with these polyols to form polyethers are ethylene oxide,propylene oxide, butylene oxide, styrene oxide and the like. These aregenerally called hydroxyl-terminated polyethers and can be linear orbranched. Examples of polyethers include polyoxyethylene glycol,polyoxypropylene glycol, polyoxytetramethylene glycol,polyoxyhexamethylene glycol, polyoxynonamethylene glycol,polyoxydecamethylene glycol, polyoxydodecamethylene glycol and mixturesthereof. Other types of polyoxyalkylene glycol ethers can be used.Especially useful polyether polyols are those derived from reactingpolyols such as ethylene glycol, diethylene glycol, triethylene glycol,1,4-butylene glycol, 1,3-butylene glycol, 1,6-hexanediol, and theirmixtures; glycerol, trimethylolethane, trimethylolpropane,1,2,6-hexanetriol, pentaerythritol, dipentaerythritol,tripentaerythritol, polypentaerythritol, sorbitol, methyl glucosides,sucrose and the like with alkylene oxides such as ethylene oxide,propylene oxide, their mixtures, and the like.

A particular class of aromatic polyisocyanates which may be employed inthe novel solvent based coating compositions of the invention arepolymethylene polyphenol isocyanates having the formula: ##STR8##wherein x equals 1 to 3. The compounds, sold under the tradename "PAPI"by the Upjohn Chemical Company of Kalamazoo, Michigan, are particularlyuseful in compositions of the invention, resulting in compositionsexhibiting desirable toughness in the final cured coating.

The active hydrogen containing blocking agents which are reacted withthe above described organic diisocyanates may be selected from numerousblocking agents which will be apparent to those skilled in this art.Preferred blocking agents include, for example, those selected from thegroup consisting of (i) aliphatic, cycloaliphatic and aromatic alkylmonoalcohols; (ii) hydroxyl amines; (iii) oximes; (iv) lactams; and (v)triazoles. Any suitable aliphatic, cycloaliphatic or aromatic alkylmonoalcohol may be used as a blocking agent in accordance with thepresent invention. For example, aliphatic alcohols, such as methyl,ethyl, chloroethyl, propyl, butyl, amyl, hexyl, heptyl, octyl, nonyl,3,3,5-trimethylhexyl, decyl, and lauryl alcohols, and the like may beemployed. Suitable cycloaliphatic alcohols include, for example,cyclopentanol, cyclohexanol and the like, while aromatic-alkyl alcoholsinclude phenylcarbinol, methylphenylcarbinol, and the like. Minoramounts of even higher molecular weight relatively non-volatilemonoalcohols may be used, if desired, to serve as plasticizers in thecoatings provided by the invention. Examples of hydroxyl amines whichmay be employed as blocking agents include ethanol amine and propanolamine. Suitable oxime blocking agents include, for example,methylethylketone oxime, acetone oxime and cyclohexanone oxime. Examplesof lactams which may be used as blocking agents are e-caprolactam,q-butyrolactam and pyrrolidone, while suitable triazoles includecompounds such as 1,2,4-triazole, 1,2,3-benzotriazole, 1,2,3-tolyltriazole and 4,5-diphenyl-1,2,3-triazole. Particularly preferred activehydrogen containing blocking agents are methylethyl ketoxime and2-ethylhexanol.

(i) Isocyanurate Ring Containing Blocked Isocyanate Compounds

Within the scope of the above general class of blocked polyisocyanatecrosslinking agents, a particular class or type of blockedpolyisocyanate crosslinking agent which may be employed in the coatingcompositions of the invention comprises isocyanurate ring containingblocked isocyanate compounds. In general, these blocked polyisocyanatesmay be formed by blocking with the aforementioned blocking agents. Thesecompounds may be formed by cyclotrimerization of difunctionalisocyanates. Usually, the reaction does not stop in this stage andcontinues through the formation of polyfunctional oligomers or a mixtureof such oligomers with a portion of the pure trifunctionalpolyisocyanate. Mixtures of trifunctional product and variouspolyfunctional oligomers are commercially available. A particularlydesirable blocked polyisocyanate crosslinking agent is the blocked formof the pure trifunctional isocyanurate represented by the followingformula: ##STR9## wherein each L is selected independently from thegroup consisting of aliphatic, cycloaliphatic and aromatic groups andcombinations thereof and B is the residue of an active hydrogencontaining blocking agent. More specifically, this compound is disclosedin U.S. patent application Ser. No. 368,178 filed April 14, 1982, thedisclosure of which is hereby incorporated by reference.

(ii) Oligoester Modified Blocked Polyisocyanates

Still further particular blocked polyisocyanates useful as crosslinkingagents in the coating compositions of this invention are oligoestermodified blocked polyisocyanates prepared from a particular class ofoligoester diols and triols. A first type of such oligoester modifiedblocked polyisocyanate is prepared from organic diisocyanates whereinone isocyanato group is more reactive than the other, with the morereactive isocyanato first being blocked with a blocking agent and theremaining isocyanato group then being reacted with hydroxylfunctionality of an oligoester diol or triol as referred to above. Thesecond type of oligoester modified blocked polyisocyanate may beprepared by reacting oligoester diols from the aforementioned class ofoligoesters with an excess of organic diisocyanate so as to form anisocyanato terminated prepolymer followed by blocking of the terminalisocyanato groups of the prepolymer with an active hydrogen containingblocking agent Each of these materials is particularly useful in thecompositions of the invention and produces final cured coatingcompositions exhibiting good flexibility.

Oligoesters of the type employed in the preparation of thesecrosslinking agents are described in U.S. Pat. No. 4,322,508 issuedMarch 30, 1982, the disclosure of which is hereby incorporated byreference. The hydroxy functional oligoesters within the useful class ofmaterials (i) have a number average molecular weight (Mn) between about150 and about 3000, preferably between about 230 and about 1000, (ii)bear 2 or 3 hydroxyl groups per molecule, and (iii) are formed by anesterification reaction between a carboxylic acid and an epoxide. Theesterification reaction products are selected from the group consistingof:

(a) the esterification reaction product of polycarboxylic acid, i.e.,carboxylic acid bearing 2 or more carboxyl groups, and monoepoxide; `(b)the esterification reaction product of polyepoxide, i.e., a compoundhaving 2 or more epoxide groups, and monocarboxylic acid, preferablycontaining no ethylenic unsaturation, and bearing no hydroxyfunctionality;

(c) the esterification reaction product of hydroxy functional carboxylicacid and monoor polyepoxide, preferably monoepoxide;

(d) the esterification reaction product of mono-carboxylic acid andhydroxy functional mono- or poly-epoxide, preferably monoepoxide; and

(e) mixtures of (a)-(d).

As noted above, the first type of oligoester modified blockedpolyisocyanate crosslinking agent is prepared by (i) reacting organicdiisocyanate bearing one isocyanato group which is more reactive thanthe other with a sufficient amount of an active hydrogen containingblocking agent to react substantially with all of the more reactiveisocyanate groups, thus providing a half-blocked diisocyanate and (ii)reacting this half-blocked intermediate with the above discussedoligoester. The organic diisocyanates employed in this synthesis, aswell as the active hydrogen containing blocking agents, are discussedabove in connection with the preparation of the isocyanurate ringcontaining blocked isocyanate cross-isocyanurate linking agents usefulin compositions of the invention. The organic polyisocyanate-blockingagent adduct intermediate is formed by reacting a sufficient quantity ofthe blocking agent with the organic diisocyanate to insure that one ofthe two -NCO groups on the diisocyanate is reacted. The reaction betweenthe organic diisocyanate and the blocking agent is exothermic and thediisocyanate and the blocking agent are preferably admixed attemperatures no higher than about 80° C., preferably below about 50° C.,to minimize the exothermic effect.

The diisocyanate/blocking agent intermediate is next reacted with theoligoester diol or triol described above so as to react substantiallyall free or unblocked isocyanato groups of the intermediate withhydroxyl groups of the oligoester. This reaction is carried outdesirably at a temperature of about 80°-120° C.

As also discussed above, the second type of oligoester modified blockedpolyisocyanate crosslinking agent useful in the novel solvent basedcoating compositions of the invention is prepared by reacting an excessof organic diisocyanate with an oligoester diol from the above describedclass of oligoesters followed by reaction of the terminal isocyanatogroups formed on the resulant prepolymer with an active hydrogencontaining blocking agent as described above so as to react withsubstantially all the isocyanato groups. The diisocyanate startingmaterial is used in excess in amounts sufficient to insure that theintermediate is isocyanate terminated. Therefore, it is preferable thatthe organic diisocyanates and the dihydroxy functional oligoester bereacted in a molar ratio of from greater than 1:1 up to 2:1. Numerousdiisocyanates of the type described hereinbefore may be employed in thepreparation of this intermediate. While it is not necessary that oneisocyanato group be more reactive than the other, the preparation ofthis type of crosslinking agent does not preclude the use of suchmaterial.

Other suitable crosslinking agents will be apparent to the skilled ofthe art in view of the present disclosure.

In the crosslinkable compositions of the invention, if an aminoplast orblocked polyisocyanate crosslinking agent is employed, it may beadvantageous in certain embodiments or for certain applications toinclude in the composition any of a variety of compatible catalystsknown to the skilled of the art to catalyze reaction of same withhydroxy, for example, for aminoplast crosslinking agent,paratoluenesulfonic acid, phosphoric acid, phenol acid phosphate, butylmaleate and the like or a compatible mixture of any of them. Exemplarycatalysts for blocked polyisocyanate crosslinking agent include theLewis acid catalysts and others known to the skilled of the art. Inaddition, a flow control agent, for example, polybutylacrylate; awetting agent, for example, silicone; pigments; a pigment dispersent;and/or a corrosion inhibitor, for example, chromate pigment, several ofall of which are known to the skilled of the art, may be employed in thecoating compositions of the invention.

Di- and polyhydroxy compounds of diverse character may be employed alsoin the composition of the invention to modify the properties of thecomposition (i.e. the properties prior to or following cure) as well asto act as solvent, including reactive solvent, for solubilizing thecrosslinking composition. Thus, for example, these compounds may impartincreased flexibility or reduce cratering in spray-applied cured filmsof the crosslinking composition of the invention. Exemplary hydroxycompounds include ethylene glycol, dipropylene glycol, 1,6-hexanediol,and polycaprolactone diols. Another class of glycols includes hydroxyterminated polybutadienes, hydrogenated bis-phenol-A, such hydroxycompounds being of generally hydrophobic character and molecular weightsof about preferably 100-5000, number average. Higher boiling solvents(e.g. boiling point above about 180° C. as 190°-250°) that are of polarcharacter may tend to interact with the resinous components ofcrosslinking composition and thereby allow higher solids content. Ifsuch hydroxy functional compounds are included in the composition of theinvention, then crosslinking agent reactive with hydroxy functionality,such as described above, may be advantageously employed.

As noted above, pigments may be used in the compositions of theinvention in accordance with known techniques. Pigments are employedmost typically, for example, to enhance the efficacy of compositionsemployed as coating compositions over corrosionsusceptible substrates.Chromate pigments, in particular, have been used to enhance corrosionprotection. It is, however, a significant advantage of the presentinvention that chromate pigments need not be employed in compositionsemployed as such coating compositions over corrosion susceptiblesubstrates. Cured coating of the invention are highly alkali resistantand provide excellent corrosion protection even without chromatepigments Such pigments and others can be employed, however, and may bedesirable for aesthetic purposes. Exemplary pigments include titaniumdioxide, silica, carbon black, and barytes and are employed typically atpigment:binder weight ratios of about 40:60 to about 60:40.

It is one characterizing aspect of the present invention that thesubstituent groups on the diene functionality and on the dieneophilefunctionality of the aminoepoxy resin employed in the compositions ofthe invention can be selected to provide the desired degree ofreactivity, that is, cure response. In particular, the degree ofreactivity is increased by diene moiety substitution groups which, innet effort, are electron donating, that is, which decrease the electronaffinity of the diene functionality conjugated double bond. Thus,reactivity is increased by substituent groups such as, for example,amine and ether linkages, sulfoxide, sulfone, urethane and the like.Similarly, it will be understood by the skilled of the art in view ofthe present disclosure, that the shelf stability of the composition isenhanced by ene moiety substitution groups which, in net effect, areelectron withdrawing, that is, which increase the electron affinity ofthe ene functionality double bond. Thus, for example, shelf life isincreased by electron withdrawing diene substitution groups such asnitro, cyano, ester ##STR10## nitrile, carbonyl, straight, branched orcyclo alkyl or cyclo alkyl or alkylene, arylene, aralkylene, --O--,--NR--, --S and the like.

It will be within the ability of those skilled in the art, in view ofthe present disclosure, to select diene substituent groups whichprovide, in net effect, the desired compromise between shelf stabilityand reactivity. It generally is preferred that no electron withdrawinggroup(s) be substituted directly on any carbon of either dienefunctionality double bond, nor on any adjacent or next adjacent atom. Incertain applications, however, a composition of the invention mayrequire extended shelf life or for some other reason call for ortolerate diene functionality comprising electron withdrawingsubstitution groups on the diene moiety.

Applications

As noted above, the self-crosslinking resin of the invention is usefulin a variety of applications including, especially, in coatingcompositions to provide an aesthetic and/or protective film on asubstrate. In particular, such crosslinkable compositions of theinvention can be formulated into a variety of primer formulationsincluding both aqueous primer formulations and non-aqueous primerformulations. Such primers can be used as coatings for bare or treatedsteels (e.g., conversion coated with phosphates) as well as for guidecoats over primers which were previously deposited, for example, byelectrodeposition. Conventional modifying ingredients can be used insuch primer formulations including, for example, flow control agents,pigments, pigment dispersents, thixotropes, anti-cratering aids,photo-stabilizers and the like, as indicated above.

Solvent Based Primers

Compositions of the invention can be dispersed in organic solvent andapplied to a substrate, for example a ferrous metal substrate, accordingto well known techniques such as by spray, curtain, dip and othercoating application methods. For solvent based coatings to be applied byspray application methods, the aminoepoxy resin preferably has numberaverage molecular weight about 1000-3000. It will be within the abilityof those skilled in the art to determine a suitable solvent and amountof same for a given coating composition of the invention, for a givenapplication. It will be understood that any solvent allowed to remain inthe cured coating should be inert to avoid adverse effects upon thecured coating or upon another coating used in conjunction with it,during the curing process or thereafter. Preferably the cured coating issubstantially free of solvent. Sufficient solvent is used to reduce theviscosity of the coating composition to a level suitable for applicationto the substrate in the desired manner. Thus, for example, for acomposition to be used as a spray-applied primer coating composition, itis preferred that sufficient solvent be used to reduce the viscosity ofthe coating composition to about 25-35 seconds, No. 4 Ford Cup at 27° C.(80° F.).

Solvent based coating compositions according to the invention are curedby heating same to a sufficient temperature for a sufficient time todrive off the solvent, to de-block the dieneophile functionality, and tocause reaction of the diene functionality with the de-blockeddieneophile functionality. Thus, for example, a solvent based coatingcomposition comprising the crosslinkable composition of the inventionaccording to preferred embodiments described above, applied by spraytechniques to the surface of an automotive vehicle body panel as aprimer coat would be cured by heating to a temperature above about 130°C. more preferably about 135°-180° C. for approximately 15-30 minutes.

Water Based Coating Compositions

The self-crosslinkable composition of the present invention can beformulated into water based coating compositions. It has been found thatcoating compositions of the invention comprising resin modified withhydroxy functional secondary amine, as disclosed above, are more easilydispersed into aqueous solvent and provide more stable aqueousdispersions. In addition, coatings, such as electrodeposited coatings ofsuch compositions are found to provide exceptionally good adhesion andresistance to corrosion.

For dispersion into aqueous solvent, the aminoepoxy resin is at leastpartially neutralized by acid, preferably weak organic acid such asformic acid, acetic acid, which is generally preferred, latic acid,butryric acid or the like or a compatible mixture of any of them.Additional suitable neutralizing acids (often referred to as"solubilizing acid") are known to the skilled of the art and will beapparent in view of the present disclosure. The at least partiallyneutralized resin is dispersed into water, preferably de-ionized waterfor use either in spray application methods, flow coating, etc. orelectrodeposition methods. Cured coatings resulting from such methodsare found to provide exceptionally good flow characteristics resultingin smooth and otherwise aesthetically superior films havingexceptionally good solvent and humidity resistance. The cured coatingswere also found to be highly alkali resistant and thus, to provideexceptionally good corrosion protection to the underlying substrate.Water based coating compositions according to the invention can beemployed in spray application techniques. Thus, for example, they can beemployed as a spray-applied primer coat for automotive vehicle bodypanels.

According to one embodiment, coating compositions of the invention canbe applied to the surface of a substrate by electrodepositiontechniques. According to this embodiment, the self-crosslinkable coatingcomposition, as described above, is at least partially, and preferablysubstantially totally neutralized with solubilizing acid and thereafterdispersed into deionized water or water/organic solvent mixture to aconcentration of about 5-25 weight percent, more preferably about 10-15weigt percent. The resulting water based composition can be used as acathodic electrocoat composition. That is, the coating comprising thecrosslinkable resin and crosslinking agent, catalysts etc., if any, willdeposit upon the workpiece acting as the cathode according to knownelectrodeposition systems and techniques. For coating compositionsadapted for cathodic electrodeposition, the diene functional aminoepoxyresin is preferably of number average molecular weight about 1000-9000,and the amine functional blocked dieneophile resin is preferably ofnumber average molecular weight about 1000-9000.

Cathodic electrodeposition according to the present invention is donepreferably at voltages of about 1-500 volts, more preferably about200-400 volts. Subsequent to electrodeposition, the coating on thesubstrate is heated to above about 130° C., more preferably about135°-180° C. for a time sufficient to effect the diene/dieneophilereaction and to drive off substantially the entire aqueous solventcontent of the coating. In general, it will be within the ability ofthose skilled in the art to select suitable electrodeposition voltageand baking temperatures and like process parameters in view of theparticular application involved

Such aqueous solvent based coating compositions can comprise a mixtureof water and water compatible solvent and diluents such as ethyleneglycols and alkylated glycols, for example oxygenated solvents such asCellosolves and carbitols and the like or a compatible mixture of any ofthem. For use as spray primers, for example, such water based coatingcompositions can be formulated with high levels of water, for example,greater than about 10%, such as about 30-50% by weight. Obviously, theparticular time and temperatures necesary to effect curing of thecoating will depend upon the particular resins employed in the coatingcompositions and will depend upon the thickness of the coating, the useof catalysts, and like parameters familiar to the skilled of the art.

The invention will be further understood by referring to the followingdetailed examples. It should be understood that these examples arepresented by way of illustration and not by way of limitation. Unlessotherwise specified, all references to "parts" are intended to meanparts by weight.

EXAMPLE I

This example illustrates the preparation of an amino maleamic acid, amonoprimary amine functional blocked dieneophile. Accordingly,3,6-endoxo-1,2,3,6-tetrahydrophthalic anhydride was first prepared bycombining 68 g (1 mole) furan with 98 g (1 mole) maleic anhydride in 166g methyl ethyl ketone. The initially clear solution was stirred at roomtemperature; a mild exotherm and the formation of a white solid wasobserved. After stirring at room temperature for 4-6 hours, the solidwas isolated by filtration, washed with cold methyl ethyl ketone anddried. To form the monoprimary amine functional blocked dieneophile, 166g (1 mole) of 3,6-endoxo-1,2,3,6-tetrahydrophthalic anhydride was addedto a solution of 170 g (1 mole) isophorone diamine in 300 g dimethoxyethane (DME). During the intial addition, the anhydride dissolved in thereaction mixture and a slight exotherm was noted. Within 4-6 hours theprecipitation of the monoprimary amine functional blocked dieneophileoccured resulting in the formation of a fine white, water soluble solidafter a thorough rinse with DME.

EXAMPLE II

This example illustrates the preparation of a self-crosslinkingdiene/dieneophile aminoepoxy resin of the present invention. Thus, 154 g(0.8 mole epoxide) Epon 828 (trademark, Shell Chemical Co., diepoxide)was dissolved in 60 g butyl Cellosolve. Furfurylamine (22.3 g) was addedand the reaction was heated to 60° C. Within about one-half hour anexotherm raised the temperature to 90° C. Heating was continued for 1hour at 60°-80° C. and then 11.15 g of diethanol amine was added and theheating was continued for another 2 hours at that temperature. Then 39 gof the amino maleamic acid of Example I was added and allowed to reactwith stirring at 80°-90° C. for 11/2 hours. It was then cooled to roomtemperature and stored.

EXAMPLE III

This example illustrates the preparation of a self-crosslinkingdiene/dieneophile aminoepoxy resin according to the present invention.Thus, 339 g (0.67 mole epoxide) Epon 1001F (trademark, Shell ChemicalCo., diepoxide) was dissolved in 100 g of butyl Cellosolve by heating to60° C. To this, 18.78 g furfurylamine, 9.34 g diethanolamine and 32.70 gof the aminomaleamic acid of Example I was added and stirred vigorously.Within about one-half hour an erotherm raised the temperature to 95° C.The reaction was allowed to continue for 1 hour while gradually reducingthe temperature to about 60° C. It was then cooled and used in preparingan unpigmented cathodically electrodepositable primer formulationaccording to the invention, as described in Example V.

EXAMPLE IV

This example illustrates the preparation of an unpigmented cathodicelectrocoat bath formulation. 100 g of the self-crosslinking aminoepoxyresin of Example II was heated to 50° C. To this 4.38 g of glacialacetic acid in 10 g of deionized water was added under stirring in adispersator. Then 340 g of deionized water was added slowly while thestirring was continued. The resulting electrocoat bath was allowed tostir overnight and then filtered. It was then electrodeposited on bareand conversion coated steel panels at voltages from about 100 v to 250 vwithout rupture.

EXAMPLE V

This example illustrates the preparation of an unpigmented cathodicelectrocoat bath formulation. 454 g of the self-crosslinking aminoepoxyresin of Example III was heated to 50° C. To this was added 10.21 g ofglacial acetic acid in 25 g of deionized water under slow stirring in adispersator. Heating was discontinued and 1575 g of deionized water wasadded over a 30 minute period under stirring. The resulting electrocoatbath was allowed to stir overnight and then filtered. It was thenelectro-deposited onto bare steel panels and also conversion coatedsteel panels at voltages from about 100 v to 400 v without rupture. Thecoatings were then baked at 150°-180° C. for 30 minutes and were foundto provide good corrosion resistance, showing about 1 mm loss ofadhesion from a scribe line in 72 hours of salt spray testing accordingto ASTM test method B117.

EXAMPLE VI

This example illustrates the preparation of a fully formulated cathodicelectrocoat bath formulation. The preparation invovles a two-partprocess.

Part A--Mill Base Preparation

Materials:

202 g self-crosslinking aminoepoxy resin of Example III

52 g Aluminum Silicate

15 g White Lead

7.5 g Carbon Black

48.0 g Cellosolve

The above materials were combined and the pigments were dispersed to aHegman Gage reading of greater than 7 by grinding with metal shot.

Part B--Dispersion/Bath Preparation

286 g Mill base (Part A)

230 g self-crosslinking aminoepoxy resin of Example III

16 g glacial acetic acid

1200 g deionized water

The above materials, except for the water, were mixed thoroughlytogether and heated to 50°-60° C. The water was then slowly added whilemixing in a dispersator. After all the water was added, the dispersionwas cooled to room temperature and mixed overnight. The resultingelectrocoat bath was filtered and electrodeposited at about 100-400volts on both bare and conversion coated steel panels, which on bakingat 150°-180° C. for 30 minutes afforded coatings showing good corrosionresistance (less than 1 mm adhesive loss in 72 hours salt spraytesting).

EXAMPLE VII

This example illustrates the preparation of a solvent based coatingformulation.

Mill Base

202 g self-crosslinking aminoepoxy resin of Example II

52 g Aluminum Silicate

15 g White Lead

7.5 g Carbon Black

48.0 g Cellosolve

The above materials are combined and the pigments are dispersed to aHegman Gage reading of greater than 7 by grinding with metal shot. Themill base is then incorporated into a coating formulation as follows:

Materials:

206 g mill base (Part A)

230 g self-crosslinking aminoepoxy resin of Example II

600 g 1:1 Methyl Amyl Ketone:Ethoxy Ethanol

The resulting formulation, after thorough mixing, is filtered andsprayed on steel panels and baked at 150°-180° C. for 30 minutes. Theresulting coatings have good corrosion resistance.

EXAMPLE VIII

This example illustrates the use of a straight chain aliphatic diaminein the preparation of monoprimary amine functional blocked dieneophile.Thus, the procedure of Example I is repeated except that 116 g (1 mole)1,6-hexane diamine is used in place of isophorone diamine. Within 4-6hours the precipitation of the monoprimary amine functional blockeddienophile occured resulting in the formation of a fine white, watersoluble solid after a thorough rinse with DME. The resulting monoprimaryamine functional blocked dieneophile is suitable for use according tothe method of Examples II and III for preparation of self-crosslinkingdiene/dieneophile aminoepoxy resin within the scope of the presentinvention.

EXAMPLE IX

This example illustrates the use of an aromatic diamine in thepreparation of the amine functional blocked dieneophile. Thus, theprocedure of Example I is repeated using 122 g (1 mole) 4,6-toluenediamine in place of isophorone diamine. Within 4-6 hours theprecipitation of the monoprimary amine functional blocked dieneophileoccured resulting in the formation of a fine white, water soluble solidafter a thorough rinse with DME. The resulting monoprimary aminefunctional blocked dieneophile is suitable for use according to themethod of Examples II and III for preparation of self-crosslinkingdiene/dieneophile aminoepoxy resin within the scope of the presentinvention.

EXAMPLE X

This example illustrates the use of unsaturated lactones in thepreparation of a monoprimary amine functional blocked dieneophile. Thus,the procedure of Example I is repeated except that one mole (98 g) ofα-angelicalactone (4-hydroxy-3-pentenoic acid β-lactone) is used inplace of maleic anhydride. Within 4-6 hours the precipitation of themonoprimary amine functional blocked dieneophile occurred resulting inthe formation of a fine white, water soluble solid after a thoroughrinse with DME. The resulting monoprimary amine functional blockeddieneophile is suitable for use according to method of Examples II andIII for preparation of self-crosslinking diene/dieneophile aminoepoxyresin within the scope of the present invention.

In view of this disclosure, many modifications of this invention will beapparent to those skilled in the art. It is intended that all suchapparent modifications fall within the true scope of this invention andbe included within the terms of the appended claims.

Industrial Applicability

It will be apparent from the foregoing that this invention hasindustrial applicability as a coating composition, especially as acathodic electrodeposition primer coating composition for sheet steeland the like used in automotive vehicles, household appliances and thelike, and other applications where the coating composition desirably hasexcellent storage stability and the cured coating desirably providesexcellent humidity and solvent resistance to protect the substrateagainst corrosion, wear and the like.

I claim:
 1. A substantially gel-free self-crosslinkable conjugated dienefunctional blocked dieneophile functional aminoepoxy resin of numberaverage molecular weight about 1000-9000, comprising the reactionproduct of (1) diepoxide with (2) reactants comprising (a) aminefunctional conjugated diene chain extending reactant, (b) aminefunctional blocked dieneophile chain extending reactant other than saidamine functional conjugated diene chain extending reactant, and (c)modifying agent comprising hydroxy functional secondary amine.
 2. Theself-crosslinkable resin of claim 1, wherein said modifying agent isselected from the group consisting of alkylalkanolamine, dialkanolamine,N-alkanolaniline, and a mixture of any of them, wherein each alkyl andalkanol moiety has from one to about ten carbons.
 3. Theself-crosslinkable resin of claim 1, wherein said modifying agentconsists essentially of diethanolamine.
 4. The self-crosslinkable resinof claim 1, wherein said diepoxide reactant for said aminoepoxy resin isselected from the group consisting of Bisphenol A-epichlorohydrin epoxyresin, Novolak epoxy resin, aliphatic epoxy resins and a compatiblemixture of any of them.
 5. The self-crosslinkable resin of claim 1,wherein said amine functional diene reactant consists essentially ofdi-secondary amine functional bis-diene.
 6. The self-crosslinkable resinof claim 1, wherein said amine functional diene reactant consistsessentially of mono-primary amine functional diene.
 7. Theself-crosslinkable resin of claim 6, wherein said amine functional dienereactant is selected from those of the general formula: ##STR11##wherein R³ is a divalent organic linking moiety containing no estergroups and no functionality substantially reactive with the diepoxidereactant.
 8. The self-crosslinkable resin of claim 6, wherein said aminefunctional diene reactant is selected from the group consisting offurfuryl amine, 2-aminomethyl-1,3-butadiene, and a mixture thereof. 9.The self-crosslinkable resin of claim 1, wherein said amine functionalblocked dieneophile reactant consists essentially of di-secondary aminefunctional bis-blocked dieneophile.
 10. The self-crosslinkable resin ofclaim 1, wherein said amine functional blocked dieneophile reactantconsists essentially of mono-primary amine functional blockeddieneophile.
 11. The self-crosslinkable resin of claim 1, wherein saidamine functional blocked dieneophile reactant consists essentially ofmono-primary amine functional blocked ene.
 12. The self-crosslinkableresin of claim 1, wherein said amine functional blocked dieneophilereactant comprises amino maleamic acid.
 13. The self-crosslinkable resinof claim 1, wherein said amine functional blocked dieneophile reactantcomprises the reaction product of diamine with3,6-endoxo-1,2,3,6-tetrahydrophthalic anhydride.
 14. Theself-crosslinkable resin of claim 1, wherein said amine functionalblocked dieneophile reactant comprises the reaction product of (i)diamine and (ii) conjugated diene blocking agent, with (iii) enereactant selected from the group consisting of maleic anhydride,unsaturated lactone of the general formula: ##STR12## wherein each R' isselected independently from H, C₁ -C₅ alkyl, and C₁ -C₅ hydroxyalkyl,and y is from 1 to about 4, and a compatible mixture of any of them. 15.The self-crosslinkable resin of claim 14, wherein said diamine isselected from those of the general formula H₂ N--R⁵ --NH₂, wherein R⁵ isa divalent organic C₂ -C₁₅ linking moiety which is substantiallyunreactive with said diepoxide, said ene reactant, and said dieneblocking agent.
 16. The self-crosslinkable resin of claim 15, whereinsaid diamine is selected from the group consisting of branched,straight, and cyclic aliphatic diamines, aromatic diamines,arylaliphatic diamines, and a compatible mixture of any of them.
 17. Theself-crosslinkable resin of claim 15, wherein said diamine is selectedfrom the group consisting of isophorone diamine, 1,3-propanediamine,1,4-butanediamine, 1,5-pentanediamine, 1,6-hexanediamine,1,2-ethylenediamine, toluene diamine, and a compatible mixture of any ofthem.
 18. The self-crosslinkable resin of claim 14, wherein saidconjugated diene blocking agent is selected from the group consisting ofconjugated aliphatic, cyclic aliphatic and heterocyclic aliphatic dienesand a mixture of any of them, wherein said diene is substantiallyunreactive with said diamine and with said ene reactant except at theene functionality thereof.
 19. The self-crosslinkable resin of claim 14,wherein said conjugated diene blocking agent is selected from the groupconsisting of furan, conjugated cycloalkadiene, conjugated C₄ -C₁₀alkadiene, and a mixture of any of them.
 20. The self-crosslinkableresin of claim 1, further comprising monofunctional end-capping reactantbearing a single functionality substantially reactive with epoxyfunctionality of said diepoxide reactant, and which is otherwisesubstantially unreactive with said diepoxide under end-capping reactionconditions.
 21. The self-crosslinkable resin of claim 20, wherein saidend-capping reactant is selected from the group consisting ofmono-secondary amine functional blocked dieneophile, monohydroxyfunctional blocked dieneophile, mono-secondary amine functional diene,monohydroxy functional diene, and a mixture of any of them.
 22. Theself-crosslinkable resin of claim 21, wherein said end-capping reactantcomprises the reaction product of conjugated diene blocking agentselected from the group consisting of furan, conjugated cycloalkadieneand a mixture of any of them, with monohydroxy functional dieneophileselected from the group consisting of hydroxypropyl methacrylate,methylol maleimide, and a mixture thereof.
 23. The self-crosslinkableresin of claim 20, wherein said monofunctional end-capping reactant isselected from the group consisting of furfuryl alcohol,2-hydroxymethyl-1,3-butadiene, and a mixture thereof.
 24. Asubstantially gel-free self-crosslinkable conjugated diene functionalblocked dieneophile functional aminoepoxy resin of number averagemolecular weight about 1000-9000, comprising the reaction product of (1)modifying agent comprising hydroxy functional secondary amine, inapproximately 1:1 amine to epoxy equivalent ratio, with (2) the reactionproduct of a 10%-20% stoichiometric excess of diepoxide with reactantscomprising (a) amine functional conjugated diene chain extendingreactant, and (b) amine functional blocked dieneophile chain extendingreactant other than said amine functional conjugated diene chainextending reactant.
 25. A solvent based crosslinkable coatingcomposition comprising:(A) substantially gel-free self-crosslinkablediene functional blocked dieneophile functional aminoepoxy resin ofnumber average molecular weight about 1000-3000, comprising the reactionproduct of (1) modifying agent comprising hydroxy functional secondaryamine, in approximately 1:1 amine to epoxy equivalent ratio, with (2)the reaction product of a 10%-20% stoichiometric excess of Bisphenol-Aepichlorohydrin diepoxide resin with reactants comprising(a) aminefunctional diene chain extending reactant selected from the groupconsisting of furfuryl amine, 2-aminomethyl-1,3-butadiene, and anymixture thereof, (b) amine functional blocked dieneophile chainextending reactant comprising the reaction product of (i) diamineselected from the group consisting of isophorone diamine,1,3-propanediamine, 1,4-butanediamine, 1,5-pentanediamine,1-6-hexanediamine, 1,2-ethylene- diamine, toluene diamine and anymixture thereof, and (ii) conjugated diene blocking agent selected fromthe group consisting of furan, conjugated cycloalkadiene, conjugated C₄-C₁₀ alkadiene, and a mixture of any of them, with (iii) ene reactantselected from the group consisting of maleic anhydride, unsaturatedlactone of the general formula: ##STR13## wherein each R' is selectedindependently from H, C₁ -C₅ alkyl, and C₁ -C₅ hydroxyalkyl, and y isfrom 1 to about 4, and a compatible mixture of any of them, and (c)monofunctional end-capping reactant selected from the group consistingof (i) furfuryl alcohol, (ii) 2-hydroxymethyl-1,3-butadiene, (iii) thereaction product of conjugated diene blocking agent selected from thegroup consisting of furan, conjugated cycloalkadiene, conjugated C₄ -C₁₀alkadiene and a mixture of any of them, with monohydroxy functionaldieneophile selected from the group consisting of hydroxypropylmethacrylate, methylol maleimide, and a mixture thereof, and (iv) amixture of any of (i)-(iii); and (B) organic solvent.
 26. The solventbased crosslinkable composition of claim 25, wherein said modifyingagent consists essentially of C₂ -C₅ dialkanolamine.
 27. A crosslinkablecomposition of matter adapted for use in electrodeposition of coatingson a substrate, which composition comprises:(A) substantially gel-freeself-crosslinkable diene functional blocked dieneophile functionalaminoepoxy resin of number average molecular weight about 1000-9000, atleast partially neutralized with solubilizing acid selected from thegroup consisting of acetic acid, lactic acid, formic acid, butyric acid,and a compatible mixture of any of them, comprising the reaction productof (1) modifying agent comprising hydroxy functional secondary amine, inapproximately 1:1 amine epoxy equivalent ratio, with (2) the reactionproduct of a 10%-20% stoichiometric excess of Bisphenol-Aepichlorohydrin diepoxide resin with reactants comprising(a) aminefunctional diene chain extending reactant selected from the groupconsisting of furfuryl amine, 2-aminomethyl-1,3-butadiene, and anymixture thereof, (b) amine functional blocked dieneophile chainextending reactant comprising the reaction product of (i) diamineselected from the group consisting of isophorone diamine,1,3-propanediane, 1,4-butanediamine, 1,5-pentanediamine,1-6-hexanediamine, 1,2-ethylenediamine, toluene diamine and any mixturethereof, and (ii) conjugated diene blocking agent selected from thegroup consisting of furan, conjugated cycloalkadiene, conjugated C₄ -C₁₀alkadiene, and a mixture of any of them, with (iii) ene reactantselected from the group consisting of maleic anhydride, unsaturatedlactone of the general formula: ##STR14## wherein each R' is selectedindependently from H, C₁ -C₅ alkyl, and C₁ -C₅ hydroxyalkyl, and y isfrom 1 to about 4, and a compatible mixture of any of them, and (c)monofunctional end-capping reactant selected from the group consistingof (i) furfuryl alcohol, (ii) 2-hydroxymethyl-1,3-butadiene, (iii) thereaction product of conjugated diene blocking agent selected from thegroup consisting of furan, conjugated cycloalkadiene, conjugated C₄ -C₁₀alkadiene and a mixture of any of them, with monohydroxy functionaldieneophile selected from the group consisting of hydroxypropylmethacrylate, methylol maleimide, and a mixture thereof, and (iv)mixture of any of (i)-(iii); and (B) aqueous solvent, said at leastpartially neutralized diene functional blocked dieneophile functionalaminoepoxy resin being dispersed in said aqueous solvent.
 28. Thecrosslinkable composition of claim 27, wherein said modifying agentconsists essentially of C₂ -C₅ dialkanolamine.